In the state of the art, deformable membrane mirrors are known which include a structure of actuators. Such mirrors are characterized by a resonance frequency which is reduced when the diameter of the membrane increases, which makes it impossible to produce deformable mirrors with a large diameter having significant performances as regards frequency response. The deformable mirrors according to the state of the prior art are limited accordingly to a compromise between the diameter of the membrane, the tension thereof and the resonance frequency thereof. As a matter of fact, it is necessary, in order to obtain a sufficient resonance frequency, to reduce the diameter or increase the tension of the membrane. This limitation results from the too important stiffness of the mirror, which does not sufficiently translate the vibration in a localised way upon the local deformation thereof.
In the state of the art, a solution has been provided which is described in the application for a patent WO 2005/050283 corresponding to a structure with actuators for the surface deformation, further comprising a deformable membrane, a mesh of actuators located opposite the face opposite the membrane, each actuator having an operating surface, a mesh of operating connections, with each operating connection being coupled to respectively an operating surface of one of the actuators of the mesh and respectively a point on the second surface opposite the operating surface, with each operating connection having an anisotropic stiffness and transmitting a motion which is perpendicular to the second surface. Although this solution makes it possible to optimise the membrane resonance frequency, it is difficult to implement. More particularly, the assembling of the various elements is made difficult, which implies high mechanical tolerances. Similarly, the deformable mirror according to this solution includes several blocks of elements. Finally, this solution requires the utilisation of a second deformable surface, which entails a non-negligible additional cost.
In the state of the art, a solution has been provided, which is described in the U.S. Pat. No. 5,831,780 and corresponds to a supporting system for a mirror including a base, a fine optical substrate having a first light collecting surface and an opposite rear surface, flexible means for coupling the rear surface of the substrate and the base together, and at least one actuator interposed in the flexible coupling means, connected between the base and the optical substrate in order to controllably modify the shape of said optical substrate, with said flexible coupling means including a flexible foundation which contains only partially at least one actuator. The main drawback of this solution is that the embodiment thereof is very difficult to implement. It cannot be applied but for mirrors having a diameter of the order of several tens of centimetres. The number of degrees of correction by the actuator is also low, since this solution only aims at compensating the deformations which the mirror would have undergone when it is sent into space. Then, the drawback of the prior art solutions lies in the impossibility, for a given diameter of the mirror, to obtain significant resonance frequencies while keeping a sufficient number of correction degrees and an easy production of the mirror.